Layer-layer lithium rich complex metal oxides with high specific capacity and excellent cycling

ABSTRACT

Lithium rich and manganese rich lithium metal oxides are described that provide for excellent performance in lithium-based batteries. The specific compositions can be engineered within a specified range of compositions to provide desired performance characteristics. Selected compositions can provide high values of specific capacity with a reasonably high average voltage. Compositions of particular interest can be represented by the formula, x Li 2 MnO 3 .(1−x) Li Ni u+Δ Mn u−Δ Co w A y O 2 . The compositions undergo significant first cycle irreversible changes, but the compositions cycle stably after the first cycle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent applicationSer. No. 12/869,976 filed on Aug. 27, 2010 to Lopez et al., entitled“Layer-Layer Lithium Rich Complex Metal Oxides with High SpecificCapacity and Excellent Cycling,” incorporated herein by reference, whichclaims priority to provisional U.S. patent application Ser. No.61/237,344 filed on Aug. 27, 2009 to Venkalachalam et al., entitled“Cathode Compositions for Lithium Ion Batteries,” incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to desirable composition ranges of complex metaloxides that provide desirable performance properties.

BACKGROUND OF THE INVENTION

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. Rechargeable batteries are also referredto as secondary batteries, and lithium ion secondary batteries generallyhave a negative electrode material that intercalates lithium. For somecurrent commercial batteries, the negative electrode material can begraphite, and the positive electrode material can comprise lithiumcobalt oxide (LiCoO₂). In practice, only roughly 50% of the theoreticalcapacity of the cathode can be used, e.g., roughly 140 mAh/g. At leasttwo other lithium-based cathode materials are also currently incommercial use. These two materials are LiMn₂O₄, having a spinelstructure, and LiFePO₄, having an olivine structure. These othermaterials have not provided any significant improvements in energydensity.

Lithium ion batteries can be classified into two categories based ontheir application. The first category involves high power battery,whereby lithium ion battery cells are designed to deliver high current(Amperes) for such applications as power tools and Hybrid ElectricVehicles (HEVs). However, by design, these battery cells are lower inenergy since a design providing for high current generally reduces totalenergy that can be delivered from the battery. The second designcategory involves high energy batteries, whereby lithium ion batterycells are designed to deliver low to moderate current (Amperes) for suchapplications as cellular phones, lap-top computers, Electric Vehicles(EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery ofhigher total capacity.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a positive electrode activecomposition for a lithium ion battery comprising a layer-layer lithiummetal oxide approximately represented by the formula x Li₂MnO₃.(1−x) LiNi_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂, x is at least about 0.03 and no more thanabout 0.47, the absolute value of Δ generally is no more than about 0.2,2u+w+y is approximately equal to 1, w is in the range from 0 to 1, u isin the range from 0 to 0.5 and y is no more than about 0.1 with theproviso that both (u+Δ) and w are not zero, wherein an optional fluorinedopant can replace no more than about 10 mole percent of the oxygen.

In a further aspect, the invention pertains to a method for synthesizinga positive electrode active composition, the method comprisingco-precipitating a precursor composition, adding a lithium source at aselected point in the process, and heating the precursor composition todecompose the precursor composition to form a metal oxide.

The precursor composition can comprise manganese as well as nickeland/or cobalt in selected amounts corresponding to a product compositionapproximately represented by the formula x Li₂MnO₃.(1−x) LiNi_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂, x is at least about 0.03 and no more thanabout 0.47, the absolute value of Δ generally is no more than about 0.2,2u+w+y is approximately equal to 1, w is in the range form 0 to 1, u isin the range from 0 to 0.5 and y is no more than about 0.1, with theproviso that both (u+Δ) and w are not 0, wherein an optional fluorinedopant can replace no more than about 10 mole percent of the oxygen.

In other embodiments, the invention pertains to a positive electrodeactive material for a lithium ion cell comprising a layered lithiummetal oxide approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2-z)F_(z), where b ranges from about0.04 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 toabout 0.15 and z ranges from 0 to 0.2, with the proviso that both α andγ are not 0, and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca,Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof, and having a dischargecapacity at the 10th cycle that is at least about 180 mAh/g whendischarged at room temperature at a discharge rate of 2 C.

In additional embodiments, the invention pertains to a lithium ionbattery comprising a negative electrode comprising a graphitic carbonactive material, a positive electrode, a separator between the positiveelectrode and the negative electrode and an electrolyte comprisinglithium ions. In some embodiments, the positive electrode activematerial exhibits a specific discharge capacity of at least about 200mAh/g discharged from 4.5 volts to 2.0 volts at a C/3 rate at roomtemperature. The battery can have an average voltage of at least about3.4 and a pulse DC electrical resistance of no more than about 6 mΩ at astate of charge of at least about 30%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a battery structure separated from acontainer.

FIG. 2 is a compositional phase diagram indicating the relative amountsof transition metals in compositions formed in the Examples.

FIG. 3 is a plot of true density as a function of X in the compositionof the positive electrode active material.

FIG. 4 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.1 cycled at 0.1C for the first two cycles, 0.2 C for cycle numbers 3 and 4, 0.33 C forcycle numbers 5 and 6, 1 C for cycle numbers 7-11, 2 C for cycle numbers12-16, 5 C for cycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 5 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.2 cycled at 0.1C for the first two cycles, 0.2 C for cycle numbers 3 and 4, 0.33 C forcycle numbers 5 and 6, 1 C for cycle numbers 7-11, 2 C for cycle numbers12-16, 5 C for cycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 6 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.3 cycled at 0.1C for the first two cycles, 0.2 C for cycle numbers 3 and 4, 0.33 C forcycle numbers 5 and 6, 1 C for cycle numbers 7-11, 2 C for cycle numbers12-16, 5 C for cycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 7 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.4 cycled at 0.1C for the first two cycles, 0.2 C for cycle numbers 3 and 4, 0.33 C forcycle numbers 5 and 6, 1 C for cycle numbers 7-11, 2 C for cycle numbers12-16, 5 C for cycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 8 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.5 cycled at 0.1C for the first two cycles, 0.2 C for cycle numbers 3 and 4, 0.33 C forcycle numbers 5 and 6, 1 C for cycle numbers 7-11, 2 C for cycle numbers12-16, 5 C for cycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 9 is a is a set of plots of specific capacity versus cycle numberof a set of lithium rich metal oxides with values of X=0.5 having acoating of 0.5 weight percent MgO cycled at 0.1 C for the first twocycles, 0.2 C for cycle numbers 3 and 4, 0.33 C for cycle numbers 5 and6, 1 C for cycle numbers 7-11, 2 C for cycle numbers 12-16, 5 C forcycle numbers 17-21 and 0.2 C for cycle numbers 22-24.

FIG. 10 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having X=0.1 for the first chargeand discharge cycle with a charge to 4.6 volts and a discharge to 2.0volts at a rate of C/10.

FIG. 11 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having X=0.2 for the first chargeand discharge cycle with a charge to 4.6 volts and a discharge to 2.0volts at a rate of C/10.

FIG. 12 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having X=0.3 for the first chargeand discharge cycle with a charge to 4.6 volts and a discharge to 2.0volts at a rate of C/10.

FIG. 13 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having X=0.4 for the first chargeand discharge cycle with a charge to 4.6 volts and a discharge to 2.0volts at a rate of C/10.

FIG. 14 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having X=0.5 for the first chargeand discharge cycle with a charge to 4.6 volts and a discharge to 2.0volts at a rate of C/10.

FIG. 15 is a plot of average voltage as a function of X in thecomposition of the positive electrode active material for coin batterieshaving a lithium metal negative electrode over the first discharge cyclefrom 4.6 volts to 2.0 volts.

FIG. 16 is a plot of specific discharge capacity as a function of X inthe composition of the positive electrode active material for coinbatteries having a lithium metal negative electrode over the firstdischarge cycle from 4.6 volts to 2.0 volts.

FIG. 17 is a plot of irreversible capacity loss as a function of X inthe composition of positive electrode active material for coin batterieshaving a lithium metal negative electrode over the first discharge cyclefrom 4.6 volts to 2.0 volts.

FIG. 18 is a graph with a set of plots of differential capacity as afunction of cell voltage for a set of coin batteries formed withpositive electrode active materials having a value of X=0.1, 0.2, 0.3,0.4 and 0.5 for the first charge and discharge cycle with a charge to4.6 volts and a discharge to 2.0 volts at a rate of C/10.

FIG. 19 is a plot of specific discharge capacity versus cycle number ofa set of lithium rich metal oxides with alternative sets of compositionshaving values of X=0.1, 0.2, 0.3, 0.4 and 0.5 cycled at 0.1 C for thefirst two cycles, 0.33 C for cycle numbers 3 and 4, 1 C for cyclenumbers 5 and 9, 2 C for cycle numbers 10-14, and 5 C for cycle numbers15-19. Composition #35 has an extra two C/5 cycles in comparison to theother compositions.

FIG. 20 is a plot of differential capacity as a function of cell voltagefor a set of coin batteries formed with an alternative set of positiveelectrode active materials having X=0.1, 0.2, 0.3, 0.4 and 0.5 for thesecond charge and discharge cycle with a charge to 4.6 volts and adischarge to 2.0 volts at a rate of C/10.

FIG. 21 is a plot of specific charge and discharge capacity as afunction of cycle for a coin battery formed with a positive electrodeactive material with X=0.5 and having an AlF₃ coating for a celldischarged from 4.6 volts to 2.0 volts with a rate of 0.1 C for cycles 1and 2, 0.2 C for cycles 3 and 4 and 0.33 C for cycles 5 to 40.

FIG. 22 is a graph with a set of plot of specific discharge capacity asa function of cycle for a coin battery formed with a positive electrodeactive material with X=0.5 and having various AlF₃ coating thicknessesfor a cell discharged from 4.6 volts to 2.0 volts with a rate of 0.1 Cfor cycles 1 and 2, 0.2 C for cycles 3 and 4 and 0.33 C for cycles 5 to40.

FIG. 23( a) is a plot of the irreversible capacity loss expressed as apercent of the initial charge specific capacity as a function of AlF₃coating thickness for coin battery formed with a positive electrodeactive material with X=0.5.

FIG. 23( b) is a plot of the irreversible capacity loss expressed inunits of mAhlg as a function of AlF₃ coating thickness for coin batteryformed with a positive electrode active material with X=0.5.

FIG. 24( a) is a plot of average voltage as a function of AlF₃ coatingthickness for coin battery formed with a positive electrode activematerial with X=0.5.

FIG. 24( b) is a plot of percent average voltage reduction resultingform the presence of the coating as a function of AlF₃ coating thicknessfor coin battery formed with a positive electrode active material withX=0.5.

FIG. 25 is a plot of percent coulombic efficiency as a function of AlF₃coating thickness for coin batteries formed with positive electrodematerial with X=0.5.

FIG. 26 is a graph with three plots of DC electrical resistance as afunction of the battery state of charge for pouch cell batteries formedwith graphitic carbon as the negative electrode active material and alithium rich positive electrode active material with X=0.3, 0.4 and 0.5.

FIG. 27 is a graph with three plots of specific discharge capacity as afunction of cycle number for coin cell batteries formed with graphiticcarbon as the negative electrode active material and a lithium richpositive electrode active material with X=0.2, 0.3 and 0.5.

FIG. 28 is a graph with three plots of average voltage as a function ofcycle number for coin cell batteries formed with graphitic carbon as thenegative electrode active material and a lithium rich positive electrodeactive material with X=0.2, 0.3 and 0.5.

DETAILED DESCRIPTION OF THE INVENTION

Specific ranges of metal oxide compositions have been identified thatprovide an improved balance between particular performance properties,such as a high specific capacity, performance at higher rates, desiredvalues of DC-resistance, average voltage and cycling properties whenincorporated into a lithium based battery. In general, the batteries areformed with a composition that can be approximately represented byLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2-z)F_(z), where A is an optionalmetal dopant and F is an optional fluorine dopant. In some embodiments,the parameters of the composition stoichiometry are consistent with acomposition that can be written as x Li₂MnO₃.(1−x) LiMO₂, where M ismixture of metals generally comprising Mn as well as Ni and/or Co,optionally with a dopant metal, and where 0<x<1. In appropriateembodiments, the two crystalline materials are believed to be integratedwithin a layer-layer superlattice structure. Ranges of compositionswithin the genus represented by the formula above have been identifiedthat provide for a large specific discharge capacity, good high rateperformance, low DC-resistance and good cycling. Based on thiscompositional engineering, positive electrode active materials can bedesigned with excellent performance for selected applications. Coatingscan further improve the performance of these positive electrode activecompositions.

The positive electrode materials described herein can be used toconstruct batteries that have a combination of excellent cyclingperformance, high specific capacity, high overall capacity, relativelyhigh average voltage, low DC-resistance down to relatively low states ofcharge and excellent rate capability. The resulting lithium ionbatteries can be used as an improved power source, particularly for highenergy applications, such as electric vehicles, plug in hybrid electricvehicles and the like. The positive electrode materials exhibit arelatively high average voltage over a discharge cycle so that thebatteries can have high power output along with a high specificcapacity. The density of the compositions generally depends on thecomposition. The tap density generally depends on the real density andthe procedure to form the material. The synthesis approaches describedhere have been shown to be suitable to form materials with a high tapdensity. As a result of a relatively high tap density and excellentcycling performance, a battery can exhibit continuing high totalcapacity when cycled. Furthermore, the positive electrode materials candemonstrate a reduced proportion of irreversible capacity loss after thefirst charge and discharge of the battery so that the cycling specificcapacity can be somewhat greater. The active materials can have anappropriate coating to provide for an improvement in cycling as well aspotentially a reduction in irreversible capacity loss and an increase inspecific capacity.

The batteries described herein are lithium-based batteries in which anon-aqueous electrolyte solution comprises lithium ions. For secondarylithium ion batteries during charge, oxidation takes place at thecathode (positive electrode) where lithium ions are extracted andelectrons are released. During discharge, reduction takes place in thecathode where lithium ions are inserted and electrons are consumed.Unless indicated otherwise, performance values referenced herein are atroom temperature.

When the corresponding batteries with the intercalation-based positiveelectrode active materials are in use, the intercalation and release oflithium ions from the lattice induces changes in the crystalline latticeof the electroactive material. As long as these changes are essentiallyreversible, the capacity of the material does not change significantlywith cycling. However, the capacity of the active materials is observedto decrease with cycling to varying degrees. Thus, after a number ofcycles, the performance of the battery falls below acceptable values,and the battery is replaced. Also, on the first cycle of the battery,generally there is an irreversible capacity loss that is significantlygreater than per cycle capacity loss at subsequent cycles. Theirreversible capacity loss is the difference between the charge capacityof the new battery and the first discharge capacity. The irreversiblecapacity loss results in a corresponding decrease in the capacity,energy and power for the cell. The irreversible capacity loss generallycan be attributed to changes during the initial charge-discharge cycleof the battery materials that may be substantially maintained duringsubsequent cycling of the battery.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M°, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or a corresponding alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

The lithium ion batteries can use a positive electrode active materialthat is lithium rich relative to a reference homogenous electroactivelithium metal oxide composition. In some embodiments, it is believedthat appropriately formed lithium-rich lithium metal oxides have acomposite crystal structure. For example, in some embodiments of lithiumrich materials, a Li₂MO₃ material may be structurally integrated witheither a layered LiM′O₂ component, in which a reference structure has Mand M′ being manganese, although particular compositions of interesthave a portion of the manganese cations substituted with othertransition metal cations with appropriate oxidation states. In someembodiments, the positive electrode material can be represented in twocomponent notation as x Li₂MO₃.(1−x)LiM′O₂ where M′ is one or more metalcations with an average valance of +3 with at least one cation being amanganese cation or a nickel cation, and where M is one or more metalcations with an average valance of +4. Generally, for compositions ofparticular interest, M can be considered to be Mn. The general class ofcompositions are described further, for example, in U.S. Pat. No.6,680,143 (the '143 patent) to Thackeray et al., entitled “Lithium MetalOxide Electrodes for Lithium Cells and Batteries,” incorporated hereinby reference.

The class of positive electrode active materials of interest can beapproximately represented with a formula:

Li_(1+b)Ni_(α)Mn_(β-δ)Co_(γ)A_(δ)O_(2-z)F_(z),  (1)

where b ranges from about 0.01 to about 0.3, α ranges from 0 to about0.4, β range from about 0.2 to about 0.65, γ ranges from about 0 toabout 0.46, δ ranges from about 0.001 to about 0.15, and z ranges from 0to about 0.2 with the proviso that both α and γ are not zero, and whereA is a metal different from Ni, Mn and Co or a combination thereof.Element A and F (fluorine) are optional cation and anion dopants,respectively. Elements A can be, for example, Mg, Sr, Ba, Cd, Zn, Al,Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, or combinations thereof. Theuse of a fluorine dopant in lithium rich metal oxides to achieveimproved performance is described in copending U.S. patent applicationSer. No. 12/569,606 (now published 2010/0086854) to Kumar et al.,entitled “Fluorine Doped Lithium Rich Metal Oxide Positive ElectrodeBattery Materials With High Specific Capacity and CorrespondingBatteries,” incorporated herein by reference.

Similar compositions have been described in U.S. application Ser. No.12/246,814 (the '814 application, now published 2010/0086853) toVenkatachalam et al. entitled “Positive Electrode Material for LithiumIon Batteries Having a High Specific Discharge Capacity and Processesfor the Synthesis of these Materials”, and U.S. application Ser. No.12/332,735 (the '735 application, now published 2010/0151332) to Lopezet al. entitled “Positive Electrode Materials for High DischargeCapacity Lithium Ion Batteries”, both incorporated herein by reference.As described in the '814 application and the '735 application,surprisingly good performances have been obtained forLi[Li_(0.2)Ni_(0.175) Co_(0.10)Mn_(0.525)]O₂ using a co-precipitationsynthesis process. As described herein, desirable properties have beenobtained with specific engineering of the positive electrode activecomposition. Also, the desired stoichiometry can be selected based onthe selected properties for the material for a particular application.

The formulas presented herein are based on the molar quantities ofstarting materials in the synthesis, which can be accurately determined.With respect to the multiple metal cations, these are generally believedto be quantitatively incorporated into the final material with no knownsignificant pathway resulting in the loss of the metals from the productcompositions. Of course, many of the metals have multiple oxidationstates, which are related to their activity with respect to thebatteries. Due to the presence of the multiple oxidation states andmultiple metals, the precise stoichiometry with respect to oxygengenerally is only roughly estimated based on the crystal structure,electrochemical performance and proportions of reactant metals, as isconventional in the art. However, based on the crystal structure, theoverall stoichiometry with respect to the oxygen is reasonablyestimated. All of the protocols discussed in this paragraph and relatedissues herein are routine in the art and are the long establishedapproaches with respect to these issues in the field.

The stoichiometric selection for the compositions can be based on somepresumed relationships of the oxidation states of the metal ions in thecomposition. As an initial matter, if in Eq. (1) approximatelyb+α+β+γ=1, then the formula of the composition can be correspondinglyapproximately written in two component notation as:

x.Li₂MO₃.(1−x)LiM′O₂,  (2)

where M is one or more metal atoms with an average oxidation state of +4and M′ is one or more metal atoms with an average oxidation state of +3.While Mn, Co and Ni have multiple accessible oxidation states, whichdirectly relates to their use in the active material, in these compositematerials if appropriate amounts of these elements are present, it isthought that the elements can have the oxidation states Mn⁺⁴, Co⁺³ andNi⁺². Then, if δ=0, the two component notation simplifies tox.Li₂MnO₃.(1−x)LiNi_(u)Mn_(u)Co_(w)O₂, with 2u+w=1. In some embodiments,the stoichiometric selection of the metal elements can be based on thesepresumed oxidation states. Based on the oxidation state of dopantelement A, corresponding modifications of the formula can be made.

However, active compositions have been found with good performanceproperties with variations in composition around the reference ranges ofcompositions described in the previous paragraph. In particular, a rangeof compositions of interest can be described approximately by theformula x.Li₂MnO₃.(1−x)LiNi_(u+Δ)Mn_(u−Δ)Co_(w)O₂, with 2u+w=1 and−0.3≦Δ≦0.3. In some embodiments of particular interest, x ranges from0.03 to about 0.47, although other ranges are of particular interest forparticular performance properties. Furthermore, in some embodiments, uranges from 0 to about 0.4, and w ranges from 0 to about 0.475, with theproviso that both u and w are not zero. A person of ordinary skill inthe art will recognize that additional composition ranges within theexplicit ranges above are contemplated and are within the presentdisclosure.

During the first charge of the lithium ion battery, irreversible changestake place in the battery. For example, at the negative electrode, asolvent electrolyte interface forms with a corresponding consumption oflithium ions. However, in the context of the lithium rich materialsdescribed herein, the changes at the positive electrode are ofparticular interest. Specifically, for the lithium rich compositionsherein, the change in the positive electrode during the first chargecontributes a majority of the irreversible capacity loss. Theirreversible capacity loss only measures structural changes to thepositive electrode active materials that result in charge generationduring the charge step since the capacity loss is measured based oncharge that flows from the positive electrode to the negative electrodeduring the charge step. Irreversible changes that do not produce currentdo not contribute to the measured irreversible capacity loss even thoughcycling capacity of the material may be reduced. The generation ofelectrons during the charge has a corresponding generation of metal ionsat the positive electrode during the charge, and if the metal ions arelithium ions, these ions are in principle available for cycling. Ifnon-lithium metal ions are formed, the dissolution of the metal directlyresults in an irreversible capacity loss and cycling degradation.Nevertheless, irreversible changes besides dissolution of non-lithiummetal can take place that result in irreversible capacity loss, such asoxygen loss. Thus, while a large portion of the initial lithium in thepositive electrode can be removed during the initial battery charging,the irreversible capacity loss indicates that all of the lithium cannotreturn to the positive electrode during discharge of the battery.

With respect to the charging of a battery with the composite materials,the lithium manganese oxide (Li₂MnO₃) component of the compositions canundergo a reaction to release molecular oxygen with an associatedrelease of 2 Li ions as indicated in equation (3):

Li₂MnO₃ →MnO ₂+2Li⁺+2e ⁻+½O₂.  (3)

Upon discharge, the MnO₂ composition takes up a single lithium ion and asingle electron to form LiMnO₂ so that there is an overall significantdecrease in capacity due to the irreversible reaction of the materialduring the initial charge. As discussed below, evidence suggests thatthe reaction in Eq. (3) takes place at voltages above 4.4 volts. Thus,with the lithium rich layer-layer material, during the first cyclecharge above 4.4V, decomposition of a Li₂MnO₃ component in the highcapacity material can lead to oxygen loss and an irreversible capacityloss. The materials in principle can undergo other irreversible changesthat may coincide with the initial charge step, such as a decompositionreaction Li₂MnO₃→MnO₂+Li₂O. Such a decomposition reaction does notresult in a measured irreversible capacity loss since no electrons aregenerated that would be measured during the initial charge, but such areaction to form inert lithium oxide could result in a loss ofreversible capacity relative to the theoretical capacity for aparticular weight of material. The initial reactions involving theactive material are not completely understood.

Based on a layer-layer material with a composition of x.Li₂MnO₃.(1−x)LiNi_(u)Mn_(u)Co_(w)O₂, two parameters of the composition are “x” andu/w. As “x” is increased, the material has a greater amount of lithiumavailable. However, as “x” increases, the irreversible capacity lossgenerally increases so that only a portion of the increased amount oflithium is available for cycling. Nevertheless, some of the increasedlithium may be available for cycling with an increase in “x” since thereversible specific capacity increases with “x” at least over a portionof the range in x. The ratio u/w relates to the relative amounts ofmanganese and nickel relative to cobalt. The relationships that havebeen found with variations of the u/w ratio are complex. Based on theobserved increase in specific capacity over a portion of the range withan increase in “x,” the layer-layer crystal structure evidentlyintroduces complexities to the structure.

Differential capacity plots over the first cycle of the battery indicatethat a first peak at voltages is observed just below 4 volts presumablyresulting from the LiM′O₂ component of the active composition while apeak in the vicinity of 4.4 volts is thought to correspond with thereduction of the Li₂MnO₃ component. The lower voltage peak has a longtail in the plot toward higher voltages suggesting that all of thelithium from the LiM′O₂ component may not be extracted when lithiumassociated with the Li₂MnO₃ component begins to be extracted. Thelayer-layer materials are likely more complex than the two componentanalysis suggests, and the high cycling capacity is consistent with amore complex structure. Similarly, the Li₂MnO₃ component would seem tocycle with the present of Mn⁺³ following charging without largedissolution of the manganese into the electrolyte, so the complexstructure would seem to result in stabilization of the structureconsistent with a more complex nature of the material. The furtherstabilization of the material when a coating is present points tofurther complexity in the structure, and this complexity producessignificant unpredictability in the results obtained herein.

In general, based on the teachings herein, specific active materialstoichiometries can be selected to obtain desired performance propertiesfor a resulting battery. For example, even though the active materialgenerally undergoes irreversible changes during the first charge of thebattery, the materials with a greater value of x can exhibit a greaterinitial low rate cycling discharge specific capacity up to a particularvalue of x. The results in the Examples below indicate that thematerials with x=0.4 exhibit a greater value of low rate specificcapacity and even higher relative specific capacities at higher ratesrelative to the materials with x=0.5. Also, other properties can besignificant so that the materials with a larger value of x generallyhave a greater irreversible capacity loss, so materials with acomposition corresponding to a lower value of x can be exploited for adecreased value of irreversible capacity loss. In addition, thematerials with a lower value of x exhibit a greater average voltage whendischarged from 4.6 volts to 2.0 volts, and a greater average voltagecan translate into greater energy delivery. It has been found that thetrue density of the material is a function of the composition. Inparticular, the true density generally is greater for cathodecompositions with lower X. This is an attractive feature to increase theelectrode density and increase volumetric energy and powerspecifications. Improving the volumetric characteristics is useful whereit is desirable to reduce cell volume, as in the case of consumerelectronics and some automotive applications.

Carbonate and hydroxide co-precipitation processes have been performedfor the desired lithium rich metal oxide materials described herein.Generally, a solution is formed from which a metal hydroxide orcarbonate is precipitated with the desired metal stoichiometry. Themetal hydroxide or carbonate compositions from co-precipitation can besubsequently heat-treated to form the corresponding metal oxidecomposition with appropriate crystallinity. The lithium cations caneither be incorporated into the initial co-precipitation process, or thelithium can be introduced in a solid state reaction during or followingthe heat treatment to form the oxide compositions from the hydroxide orcarbonate compositions. As demonstrated in the examples below, theresulting lithium rich metal oxide materials formed with theco-precipitation process have improved performance properties. Asdescribed in the '735 application above, the co-precipitation processescan be adapted to provide lithium metal oxide powders with a relativelyhigh tap density, which can be exploited with respect to improvedperformance for a specific battery volume.

Metal fluoride coatings can provide significant improvements for lithiumrich layered positive electrode active materials described herein. Theseimprovements relate to long term cycling with significantly reduceddegradation of capacity, a significant decrease in first cycleirreversible capacity loss and an improvement in the capacity generally.The thickness of coating material can be selected to accentuate theobserved performance improvements. Metal fluoride coatings designed forexcellent performance with lithium rich metal oxides are describedfurther in copending U.S. patent application Ser. No. 12/616,226, nowpublished 2011/0111298 to Lopez et al., entitled “Coated PositiveElectrode Materials for Lithium Ion Batteries,” incorporated herein byreference.

Also, metal oxides and metal phosphates have also been used as coatingsfor positive electrode active materials. In the Examples below, resultsare presented with a coating of MgO for various active compositionsalong with some results with AlF₃ coatings. Metal oxide coatings for useon lithium rich metal oxide active materials are described further incopending U.S. patent application 2011/0076556 to Karthikeyan et al.,entitled “Metal Oxide Coated Positive Electrode Materials ForLithium-Based Batteries,” incorporated herein by reference.

The use of a coating can provide a decrease in the irreversible capacityloss, although the MgO coatings in the Examples below generally do notresult in a significant decrease in irreversible capacity loss. Inaddition to suggesting reduced changes to the material structure, thedecrease in irreversible capacity loss can be advantageous in increasingthe energy and power density of a battery. In some embodiments, thecoating can result in an increase the specific capacity and the averagevoltage. These observations suggest that significant differences maytake place with respect to changes to the active material in the firstcharge due to the presence of the coating. These changes are not yetwell understood. The increase in cycling discharge capacity due to thecoating is clearly directly advantageous with respect to batteryperformance. Also, the coatings can significantly improve the cyclingperformance of the battery.

It is useful to note that during charge/discharge measurements, thespecific capacity of a material depends on the rate of discharge. Themaximum specific capacity of a particular material is measured at veryslow discharge rates. In actual use, the actual specific capacity isless than the maximum due to discharge at a finite rate. More realisticspecific capacities can be measured using reasonable rates of dischargethat are more similar to the rates during use. For low to moderate rateapplications, a reasonable testing rate involves a discharge of thebattery over three hours. In conventional notation this is written asC/3 or 0.33 C, and other charge and discharge rates can be written inthis notation.

Rechargeable batteries have a range of uses, such as mobilecommunication devices, such as phones, mobile entertainment devices,such as MP3 players and televisions, portable computers, combinations ofthese devices that are finding wide use, as well as transportationdevices, such as automobiles and fork lifts. Most of the batteries usedin these electronic devices have a fixed volume. It is therefore highlydesirable that the positive electrode material used in these batterieshas a high tap density so there is essentially more chargeable materialin the positive electrode yielding a higher total capacity of thebattery. The batteries described herein that incorporate improvedpositive electrode active materials having good properties with respectto specific capacity, tap density, and cycling can provide improvedperformance for consumers, especially for medium current applications.

The batteries described herein are suitable for vehicle applications. Inparticular, these batteries can be used in battery packs for hybridvehicles, plug-in hybrid vehicles and purely electric vehicles. Thesevehicles generally have a battery pack that is selected to balanceweight, volume and capacity. Thus, due to the high capacity of thebatteries described herein, a battery pack that yields a desired amountof total power can be made in a reasonable volume, and these batterypacks can correspondingly achieve the excellent cycling performance.

Positive Electrode Active Materials

The positive electrode active materials comprise lithium richcompositions that generally are believed to form a layered compositecrystal structure. In embodiments of particular interest, the lithiummetal oxide compositions further comprise Ni, Co and Mn ions with anoptional metal dopant. As described herein, the metal stoichiometry canbe adjusted to achieve desirable performance properties for resultingbatteries incorporating the active materials in the positive electrodes.As noted above, the positive electrode composition can comprise anoptional fluorine anion dopant. The presence or absence of a fluorinedopant is not expected to significantly change the issues surroundingthe selection of metal cation stoichiometry for the compositions, andthe following discussion generally does not include the optionalfluorine dopant in the formulas to simplify the discussion. In someembodiments, it is desirable to provide an inert inorganic coating tofurther stabilize the materials. Coatings are described further in othersections below.

The positive electrode active materials of particular interest can berepresented approximately in two component notation as x Li₂MnO₃.(1−x)LiMO₂, where M is two or more metal elements with an average valance of+3 and with one of the metal elements being Mn and with another metalelement being Ni and/or Co. In general, 0<x<1, but in some embodiments0.03≦x≦0.47, in further embodiments 0.075≦x≦0.46, in additionalembodiments 0.1≦x≦0.45, and in other embodiments 0.15≦x≦0.425. Infurther embodiments, desired ranges of x can be selected based oncertain performance parameters, such as long term cycling, averagevoltage or DC electrical resistance. Thus, depending on the particularperformance parameters selected for particular interest, 0.24≦x≦0.4, infurther embodiments 0.25≦x≦0.375, and in other embodiments 0.26≦x≦0.36.Similarly, in with an emphasis on other performance parameters,0.15≦x≦0.325, in further embodiments 0.16≦x≦0.32, and in additionalembodiments 0.175≦x≦0.31. A person of ordinary skill in the art willrecognize that additional ranges of the composition parameter x withinthe explicit ranges above are contemplated and are within the presentdisclosure. For example, M can be a combination of nickel, cobalt andmanganese, which can be in oxidation states Ni⁺², Co⁺³ and Mn⁺⁴. Theoverall formula for these compositions can be written asLi_(2(1+x)/(2+x))Mn_(2x/(2+x))M_((2−2x)/(2+x))O₂. In the overallformula, the total amount of manganese has contributions from bothconstituents listed in the two component notation. Thus, in some sensethe compositions are manganese rich.

In general, M is a combination of manganese as well as nickel and/orcobalt, and optionally one or more dopant metals. Thus, M can be writtenas Ni_(u)Mn_(v)Co_(w)A_(y). For embodiments in which y=0, thissimplifies to Ni_(u)Mn_(v)Co_(w). If M includes Ni, Co, Mn, andoptionally A the composition can be written alternatively in twocomponent notation and single component notation as the following.

xLi₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂,  (4)

Li_(1+b) Ni _(α)Mn_(β)Co_(γ)A_(δ)O₂,  (5)

with u+v+w+y≈1 and b+α+β+γ+δ≈1. The reconciliation of these two formulasleads to the following relationships:

b=x/(2+x),

α=2 u(1−x)/(2+x),

β=2x/(2+x)+2v(1−x)/(2+x),

γ=2w(1−x)/(2+x),

δ=2y(1−x)/(2+x),

and similarly,

x=2b/(1−b),

u=α/(1−3b),

v=(β−2b)/(1−3b),

w=γ/(1−3b),

y=δ/(1−3b).

In some embodiments, it is desirable to have u≈v, such that LiNi_(u)Mn_(v)Co_(w)A_(y)O₂ becomes approximately LiNi_(u)Mn_(v)Co_(w)A_(y)O₂. In this composition, when y=0, the averagevalance of Ni, Co and Mn is +3, and if u≈v, then these elements can bebelieved to have valances of approximately Ni⁺², Co⁺³ and Mn⁺⁴. When thelithium is hypothetically fully extracted, all of the elements go to a+4 valance. A balance of Ni and Mn can provide for Mn to remain in a +4valance as the material is cycled in the battery. This balance avoidsthe formation of Mn⁺³, which has been associated with dissolution of Mninto the electrolyte and a corresponding loss of capacity.

As noted above the Li₂MnO₃ component may give off molecular oxygen uponextraction of the lithium with the resulting formation of MnO₂, whichthen could cycle with LiMnO₂ upon recharging of the battery. In thesematerials, the resulting Mn⁺³ seems to be relatively stable with respectto dissolution if Mn⁺³ is formed from the Li₂MnO₃. Since the initialcomposition loses two lithium atoms with the generation of 2 electronsand since the product composition has only a single lithium atom tocycle with the exchange of a single electron, this composition changeresults in the irreversible capacity loss. Furthermore, evidencesuggests more complex changes to the crystal structure during the firstcycle formation step so that the amount of oxygen loss may notcorrespond to the stoichiometric amount of active Li₂MnO₃ based on theamount of metal incorporated into the composition. Also, coating of thecomposition with an inorganic coating material further influences thischemistry, as evidenced by the change in the specific capacity as wellas the irreversible capacity loss. Furthermore, for coated samples, theaverage voltage can increase relative to uncoated samples. Theunderlying chemistry contributing to the excellent performance of thesematerials is not completely understood.

With respect to the one component notation, the lithium rich metal oxidecompositions of particular interest can be described by the formulaLi_(1+b)Ni_(α)Mn_(β-δ)Co_(γ)A_(δ)O₂, where b ranges from about 0.015 toabout 0.19, α ranges from 0 to about 0.4, β ranges from about 0.2 toabout 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 toabout 0.1 with the proviso that both α and γ are not zero, and where Ais Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, orcombinations thereof. In some embodiments, α ranges from about 0.1 toabout 0.3, β range from about 0.3 to about 0.65, γ ranges from about0.05 to about 0.4. With respect to the amount of dopant A present in thecomposition, in further embodiments δ ranges from about 0.001 to about0.09 and in additional embodiments from about 0.005 to about 0.075. Aperson of ordinary skill in the art will recognize that additionalranges of parameter values within the explicit ranges above arecontemplated and are within the present disclosure.

In embodiments in which the sum b+α+β+γ+δ in the formula for thepositive electrode active material approximately equals 1.0, then thecomposition can necessarily be written in the two component notationnoted above. However, even if the composition can be written in twocomponent notation, the crystal structure of the composition does notnecessarily have components indicative of the different materials. Datain the examples below provides evidence that, at least for some of theembodiments, x-ray diffraction lines corresponding to Li₂MnO₃ can beobserved along with lines corresponding to LiMO₂.

With respect to some embodiments of materials described herein,Thackeray and coworkers have proposed a composite crystal structure forsome lithium rich metal oxide compositions in which a Li₂MO₃ compositionis structurally integrated into a layered structure with a LiM′O₂component. Batteries formed from these materials have been observed tocycle at high voltages and with higher capacities relative to batteriesformed with corresponding LiMO₂ compositions. These materials aredescribed generally in U.S. Pat. No. 6,680,143 to Thackeray et al.,entitled Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” and U.S. Pat. No. 6,677,082 to Thackeray et al., entitled“Lithium Metal Oxide Electrodes for Lithium Cells and Batteries,” bothof which are incorporated herein by reference. Thackeray identified Mn,Ti, and Zr as being of particular interest as M′ and Mn and Ni for M.

The structure of some specific layered structures is described furtherin Thackeray et al., “Comments on the structural complexity oflithium-rich Li_(1+x)M_(1-x)O₂ electrodes (M=Mn,Ni,Co) for lithiumbatteries,” Electrochemistry Communications 8 (2006), 1531-1538,incorporated herein by reference. The study reported in this articlereviewed compositions with the formulasLi_(1+x)[Mn_(0.5)Ni_(0.5)]_(1-x)O₂ and Li_(1+x)[Mn_(0.333)Ni_(0.333)Co_(0.333]) _(1-x)O₂. The article also describes the structuralcomplexity of the layered materials.

Recently, Kang and coworkers described a composition for use insecondary batteries with the formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M′_(δ)O_(2-z)F_(z), M′=Mg, Zn, Al, Ga, B, Zr,Ti, x between about 0 and 0.3, α between about 0.2 and 0.6, β betweenabout 0.2 and 0.6, γ between about 0 and 0.3, δ between about 0 and 0.15and z between about 0 and 0.2. The metal ranges and fluorine wereproposed as improving battery capacity and stability of the resultinglayered structure during electrochemical cycling. See U.S. Pat. No.7,205,072, to Kang et al. (the '072 patent), entitled “Layered cathodematerials for lithium ion rechargeable batteries,” incorporated hereinby reference. This reference reported a cathode material with a capacitybelow 250 mAh/g (milli-ampere hours per gram) at room temperature after10 cycles, which is at an unspecified rate that can be assumed to be lowto increase the performance value. Kang et al. examined various specificcompositions including Li_(1.2)Ni_(0.15)Mn_(0.55) CO_(0.10)O₂, whichcorresponds with an x=0.5 composition. The effects of fluorine dopingfor lithium rich and manganese rich lithium metal oxides is describedfurther in published U.S. patent application 2010/0086854 to Kumar etal., entitled “Fluorine Doped Lithium Rich Metal Oxide PositiveElectrode Battery Materials With High Specific Capacity andCorresponding Batteries,” incorporated herein by reference.

The results obtained in the '072 patent involved a solid state synthesisof the materials that did not achieve comparable cycling capacity of thebatteries formed with cathode active materials formed withco-precipitation methods. The improved performance of the materialsformed by co-precipitation is described further in the '814 applicationand '735 application noted above as well as in US 2010/0086854 forfluorine doped compositions. The co-precipitation process for the dopedmaterials described herein is described further below.

The performance of the positive electrode active materials is influencedby many factors. As described herein, the compositions of the materialscan be selected to achieve desired performance parameters for aparticular battery application. In particular, it is believed that thecompositions with u≈v in the formula above results in relatively stablecycling. This observation would be consistent with results observed inthe '814 application and the '735 application, the compositions in the'814 application and the '735 application had stoichiometries somewhatvaried from u≈v. Also, since the Li₂MnO₃ component can resultpotentially in some amount of Mn+3 that can cycle relatively stably inthe complex lattice of the lithium rich and manganese rich compositionsdescribed herein.

Based on these observations and the results in the examples below, thecomposition of particular interested can be represented approximately bythe formula:

xLi₂MnO₃.(1−x)LiNi_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂,  (6)

where the absolute value of Δ generally is no more than about 0.3(−0.3≦Δ≦0.3), in some embodiments no more than about 0.2 (−0.2≦Δ≦0.2),in other embodiments 0.175 (−0.175≦Δ≦0.175) and in further embodimentsno more than about 0.15 (−0.15≦Δ≦0.15). Desirable ranges for x are givenabove. With 2u+w+y≈1, desirable ranges of parameters are in someembodiments 0≦w≦1, 0≦u≦0.5, 0≦y≦0.1 (with the proviso that both u and ware not zero), in further embodiments, 0.1≦w≦0.6, 0.1≦u≦0.45, 0≦y≦0.075,and in additional embodiments 0.24≦w≦0.475, 0.25≦u≦0.4, 0≦y≦0.05. Eachset of values within these ranges can be independently selected toachieve desired performance values and compositions for each value of xwithin the specific ranges of x described in detail above. A person ofordinary skill in the art will recognize that additional ranges ofcomposition parameters within the explicit ranges above are contemplatedand are within the present disclosure. As used herein, the notation(value1≦variable≦value2) implicitly assumes that value 1 and value 2 areapproximate quantities.

The mean particle size and the particle size distribution are two of thebasic properties characterizing the positive electrode active materials,and these properties influence the rate capabilities and tap densitiesof the materials. Because batteries have fixed volumes, it is thereforedesirable that the material used in the positive electrode of thesebatteries has a high tap density if the specific capacity of thematerial can be maintained at a desirably high value. Then, the totalcapacity of the battery can be higher due to the presence of morechargeable material in the positive electrode. The synthesis approachesdescribed in the following section have been found to have thecapability of producing powders of the active materials described hereinwith appropriate tap densities to provide resulting batteries withdesired performance for most commercial applications.

Synthesis Methods

Synthesis approaches described herein can be used to form layer-layerlithium rich positive electrode active materials with high values ofspecific capacity and a relatively high tap density. The synthesismethods have been adapted for the synthesis of compositions with theformula Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2-z)F_(z) and the desiredparameter ranges, as described above. The synthesis approaches are alsosuitable for commercial scale up. Specifically, co-precipitation processcan be used to synthesize the desired lithium rich positive electrodematerials with desirable results.

In the co-precipitation process, metal salts are dissolved into anaqueous solvent, such as purified water, with a desired molar ratio.Suitable metal salts include, for example, metal acetates, metalsulfates, metal nitrates, and combination thereof. The concentration ofthe solution is generally selected between 1 M and 3 M. The relativemolar quantities of metal salts can be selected based on the desiredformula for the product materials. Similarly, the optional dopantelements can be introduced along with the other metal salts at theappropriate molar quantity such that the dopant is incorporated into theprecipitated material. The pH of the solution can then be adjusted, suchas with the addition of Na₂CO₃ and/or ammonium hydroxide, to precipitatea metal hydroxide or carbonate with the desired amounts of metalelements. Generally, the pH can be adjusted to a value between about 6.0to about 12.0. The solution can be heated and stirred to facilitate theprecipitation of the hydroxide or carbonate. The precipitated metalhydroxide or carbonate can then be separated from the solution, washedand dried to form a powder prior to further processing. For example,drying can be performed in an oven at about 110° C. for about 4 to about12 hours. A person of ordinary skill in the art will recognize thatadditional ranges of process parameters within the explicit ranges aboveare contemplated and are within the present disclosure.

The collected metal hydroxide or carbonate powder can then be subjectedto a heat treatment to convert the hydroxide or carbonate composition tothe corresponding oxide composition with the elimination of water orcarbon dioxide. A fluoride, such as MgF₂, can be added to introduce afluoride dopant. Generally, the heat treatment can be performed in anoven, furnace or the like. The heat treatment can be performed in aninert atmosphere or an atmosphere with oxygen present. In someembodiments, the material can be heated to a temperature of at leastabout 350° C. and in some embodiments from about 400° C. to about 800°C. to convert the hydroxide or carbonate to an oxide. The heat treatmentgenerally can be performed for at least about 15 minutes, in furtherembodiments from about 30 minutes to 24 hours or longer, and inadditional embodiments from about 45 minutes to about 15 hours. Afurther heat treatment can be performed to improve the crystallinity ofthe product material. This calcination step for forming the crystallineproduct generally is performed at temperatures of at least about 650°C., and in some embodiments from about 700° C. to about 1200° C., and infurther embodiments from about 700° C. to about 1100° C. The calcinationstep to improve the structural properties of the powder generally can beperformed for at least about 15 minutes, in further embodiments fromabout 20 minutes to about 30 hours or longer, and in other embodimentsfrom about 1 hour to about 36 hours. The heating steps can be combined,if desired, with appropriate ramping of the temperature to yield desiredmaterials. A person of ordinary skill in the art will recognize thatadditional ranges of temperatures and times within the explicit rangesabove are contemplated and are within the present disclosure.

The lithium element can be incorporated into the material at one or moreselected steps in the process. For example, a lithium salt can beincorporated into the solution prior to or upon performing theprecipitation step through the addition of a hydrated lithium salt. Inthis approach, the lithium species is incorporated into the hydroxide orcarbonate material in the same way as the other metals. Also, due to theproperties of lithium, the lithium element can be incorporated into thematerial in a solid state reaction without adversely affecting theresulting properties of the product composition. Thus, for example, anappropriate amount of lithium source generally as a powder, such asLiOH.H₂O, LiOH, Li₂CO₃, or a combination thereof, can be mixed with theprecipitated metal carbonate or metal hydroxide. The powder mixture isthen advanced through the heating step(s) to form the oxide and then thecrystalline final product material.

Further details of the hydroxide co-precipitation process are describedin the '814 application referenced above. Further details of thecarbonate co-precipitation process are described in the '735 applicationreferenced above.

Coatings and Methods for Forming the Coatings

Inorganic coatings, such as metal fluoride coatings and metal oxidecoatings, have been found to significantly improve the performance ofthe lithium rich layered positive electrode active materials describedherein, although the coatings are believed to be inert with respect tobattery cycling. In particular, the cycling properties of the batteriesformed from metal fluoride coated lithium metal oxide have been found tosignificantly improve from the uncoated material, although inert metaloxide coatings and metal phosphate coatings have also been found toyield desirable properties. Additionally, the specific capacity of thebatteries also shows desirable properties with the coatings, and theirreversible capacity loss of the first cycle of the battery can bereduced. As discussed above, first cycle irreversible capacity loss of abattery is the difference between the charge capacity of the new batteryand its first discharge capacity. For the batteries described herein,significant portion of the first cycle irreversible capacity loss isgenerally attributed to the positive electrode material. When thecoating is appropriately selected, these advantageous properties fromthe coating are maintained for the compositions described herein withspecifically selected stoichiometries to achieve desired performanceparameters.

In the Examples below, performance properties are obtained for theactive materials coated with magnesium oxide, MgO, and with aluminumfluoride, AlF₃. The magnesium oxide coatings provide for an increase inthe specific capacity of the active material, and the magnesium oxidecoatings can be expected to improve the longer term cycling propertiesof the positive electrode active materials. However, the MgO coatings donot result in a decrease of the irreversible capacity loss of thematerials. The AlF₃ coatings are found to decrease irreversible capacityloss as well as to increase the specific capacity.

In general, other metal oxide coatings, as an alternative to MgO, canalso be used effectively, and other metal fluorides or metalloidfluorides can also be used for the coating. Similarly, a coating with acombination of metal and/or metalloid elements can be used. Suitablemetals and metalloid elements for the fluoride coatings include, forexample, Al, Bi, Ga, Ge, In, Mg, Pb, Si, Sn, Ti, Tl, Zn, Zr andcombinations thereof. Aluminum fluoride can be a desirable coatingmaterial since it has a reasonable cost and is consideredenvironmentally benign. The metal fluoride coating are describedgenerally in published PCT application WO 2006/109930A to Sun et al.,entitled “Cathode Active Materials Coated with Fluorine Compound forLithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. It has been found that metal/metalloidfluoride coatings can significantly improve the performance of lithiumrich layered compositions for lithium ion secondary batteries. See, forexample, the '814 application and the '735 application cited above, aswell as copending U.S. patent application Ser. No. 12/616,226, nowpublished 2011/0111298 to Lopez et al., entitled “Coated PositiveElectrode Materials for Lithium Ion Batteries,” which is incorporatedherein by reference.

An increase in capacity and a reduction in irreversible capacity losswere noted with Al₂O₃ coatings by Wu et al., “High Capacity,Surface-Modified Layered Li[Li_((1-x)/3)Mn_((2-x)/3)Ni_(x/3)Co_(x/3)]O₂Cathodes with Low Irreversible Capacity Loss,” Electrochemical and SolidState Letters, 9 (5) A221-A224 (2006), incorporated herein by reference.The use of a LiNiPO₄ coating to obtain improved cycling performance isdescribed in an article to Kang et al. “Enhancing the rate capability ofhigh capacity xLi₂MnO₃ (1−x)LiMO₂ (M=Mn, Ni, Co) electrodes by Li—N₁—PO₄treatment,” Electrochemistry Communications 11, 748-751 (2009),incorporated herein by reference, and this article can be referencedgenerally with respect to the formation of metal phosphate coatings.

In some embodiments, the coating improves the specific capacity of thebatteries even though the coating itself is not electrochemicallyactive. However, the coatings also influence other properties of theactive material, such as the average voltage, thermal stability andimpedance. The selection of the coating properties can incorporateadditional factors related to the overall range of properties of thematerial.

In general, the coatings can have an average thickness of no more than25 nm, in some embodiments from about 0.5 nm to about 20 nm, in otherembodiments from about 1 nm to about 12 nm, in further embodiments from1.25 nm to about 10 nm and in additional embodiments from about 1.5 nmto about 8 nm. A person of ordinary skill in the art will recognize thatadditional ranges of coating material within the explicit ranges aboveare contemplated and are within the present disclosure. The amount ofAlF₃ effective in AlF₃ coated metal oxide materials to improve thecapacity of the uncoated material is related to the particle size andsurface area of the uncoated material. Further discussion of the effectson the performance properties for coated lithium rich lithium metaloxides is found in copending U.S. patent application Ser. No.12/616,226, now published 2011/0111298 to Lopez et al., entitled “CoatedPositive Electrode Materials for Lithium Ion Batteries,” incorporatedherein by reference.

A metal fluoride coating can be deposited using a solution basedprecipitation approach. A powder of the positive electrode material canbe mixed in a suitable solvent, such as an aqueous solvent. A solublecomposition of the desired metal/metalloid can be dissolved in thesolvent. Then, NH₄F can be gradually added to the dispersion/solution toprecipitate the metal fluoride. The total amount of coating reactantscan be selected to form the desired thickness of coating, and the ratioof coating reactants can be based on the stoichiometry of the coatingmaterial. The coating mixture can be heated during the coating processto reasonable temperatures, such as in the range from about 60° C. toabout 100° C. for aqueous solutions for from about 20 minutes to about48 hours, to facilitate the coating process. After removing the coatedelectroactive material from the solution, the material can be dried andheated to temperatures generally from about 250° C. to about 600° C. forabout 20 minutes to about 48 hours to complete the formation of thecoated material. The heating can be performed under a nitrogenatmosphere or other substantially oxygen free atmosphere.

An oxide coating is generally formed through the deposition of aprecursor coating onto the powder of active material. The precursorcoating is then heated to form the metal oxide coating. Suitableprecursor coating can comprise corresponding metal hydroxides, metalcarbonates or metal nitrates. The metal hydroxides and metal carbonateprecursor coating can be deposited through a precipitation process sincethe addition of ammonium hydroxide and/or ammonium carbonate can be usedto precipitate the corresponding precursor coatings. A metal nitrateprecursor coating can be deposited through the mixing of the activecathode powder with a metal nitrate solution and then evaporating thesolution to dryness to form the metal nitrate precursor coating. Thepowder with a precursor coating can be heated to decompose the coatingfor the formation of the corresponding metal oxide coating. For example,a metal hydroxide or metal carbonate precursor coating can be heated toa temperature from about 300° C. to about 800° C. for generally fromabout 1 hr to about 20 hrs. Also, a metal nitrate precursor coatinggenerally can be heated to decompose the coating at a temperature fromabout 250° C. to about 550° C. for at least about 30 minutes. A personof ordinary skill in the art can adjust these processing conditionsbased on the disclosure herein for a specific precursor coatingcomposition.

Battery Structure

Referring to FIG. 1, a battery 100 is shown schematically having anegative electrode 102, a positive electrode 104 and a separator 106between negative electrode 102 and positive electrode 104. A battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte incontact with the electrodes provides ionic conductivity through theseparator between electrodes of opposite polarity. A battery generallycomprises current collectors 108, 110 associated respectively withnegative electrode 102 and positive electrode 104.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal is its light weight and the factthat it is the most electropositive metal, and aspects of these featurescan be advantageously captured in lithium ion batteries also. Certainforms of metals, metal oxides, and carbon materials are known toincorporate lithium ions into its structure through intercalation,alloying or similar mechanisms. Desirable mixed metal oxides aredescribed further herein to function as electroactive materials forpositive electrodes in secondary lithium ion batteries. Lithium ionbatteries refer to batteries in which the negative electrode activematerial is a material that takes up lithium during charging andreleases lithium during discharging. If elemental lithium metal itselfis used as the anode, the resulting battery generally is simply referredto as a lithium battery.

The nature of the negative electrode intercalation material influencesthe resulting voltage of the battery since the voltage is the differencebetween the half cell potentials at the cathode and anode. Suitablenegative electrode lithium intercalation compositions can include, forexample, graphite, synthetic graphite, coke, fullerenes, niobiumpentoxide, tin alloys, silicon, titanium oxide, tin oxide, and lithiumtitanium oxide, such as Li_(x)TiO₂, 0.5<x≦1 or Li_(1+x)Ti_(2-x)O₄,0≦x≦⅓. Additional negative electrode materials are described inpublished U.S. patent applications 2010/0119942 to Kumar, entitled“Composite Compositions, Negative Electrodes with Composite Compositionsand Corresponding Batteries,” and 2009/0305131 to Kumar et al., entitled“High Energy Lithium Ion Batteries with Particular Negative ElectrodeCompositions,” both of which are incorporated herein by reference.

The positive electrode active compositions and negative electrode activecompositions generally are powders that are held together in thecorresponding electrode with a polymer binder. The binder provides ionicconductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride, polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates, rubbers, e.g.ethylene-propylene-diene monomer (EPDM) rubber or styrene butadienerubber (SBR), copolymers thereof, or mixtures thereof. The particleloading in the binder can be large, such as greater than about 80 weightpercent. To form the electrode, the powders can be blended with thepolymer in a suitable liquid, such as a solvent for the polymer. Theresulting paste can be pressed into the electrode structure. In someembodiments, the batteries can be constructed based on the methoddescribed in published U.S. patent application 2009/0263707 to Buckleyet al, entitled “High Energy Lithium Ion Secondary Batteries”,incorporated herein by reference.

The positive electrode composition, and possibly the negative electrodecomposition, generally also comprises an electrically conductive powderdistinct from the electroactive composition. Suitable supplementalelectrically conductive powders include, for example, graphite, carbonblack, metal powders, such as silver powders, metal fibers, such asstainless steel fibers, and the like, and combinations thereof.Generally, a positive electrode can comprise from about 1 weight percentto about 25 weight percent, and in further embodiments from about 2weight percent to about 15 weight percent distinct electricallyconductive powder. A person of ordinary skill in the art will recognizethat additional ranges of amounts of electrically conductive powderswithin the explicit ranges above are contemplated and are within thepresent disclosure.

The electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. The current collector can comprisemetal, such as a metal foil or a metal grid. In some embodiments, thecurrent collector can be formed from nickel, aluminum, stainless steel,copper or the like. The electrode material can be cast as a thin filmonto the current collector. The electrode material with the currentcollector can then be dried, for example in an oven, to remove solventfrom the electrode. In some embodiments, the dried electrode material incontact with the current collector foil or other structure can besubjected to a pressure from about 2 to about 10 kg/cm² (kilograms persquare centimeter).

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. Commercial separator materialsare generally formed from polymers, such as polyethylene and/orpolypropylene that are porous sheets that provide for ionic conduction.Commercial polymer separators include, for example, the Celgard® line ofseparator material from Hoechst Celanese, Charlotte, N.C. Also,ceramic-polymer composite materials have been developed for separatorapplications. These composite separators can be stable at highertemperatures, and the composite materials can significantly reduce thefire risk. The polymer-ceramic composites for separator materials aredescribed further in U.S. patent application 2005/0031942A to Hennige etal., entitled “Electric Separator, Method for Producing the Same and theUse Thereof,” incorporated herein by reference. Polymer-ceramiccomposites for lithium ion battery separators are sold under thetrademark Separion® by Evonik Industries, Germany.

We refer to solutions comprising solvated ions as electrolytes, andionic compositions that dissolve to form solvated ions in appropriateliquids are referred to as electrolyte salts. Electrolytes for lithiumion batteries can comprise one or more selected lithium salts.Appropriate lithium salts generally have inert anions. Suitable lithiumsalts include, for example, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride, lithium difluoro oxalato borate,and combinations thereof. Traditionally, the electrolyte comprises a 1 Mconcentration of the lithium salts.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent generally does notdissolve the electroactive materials. Appropriate solvents include, forexample, propylene carbonate, dimethyl carbonate, diethyl carbonate,2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethylcarbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof. Particularly useful solvents for high voltagelithium-ion batteries are described further in copending U.S. patentapplication Ser. No. 12/630,992, now published 2011/0136019 filed onDec. 4, 2009 to Amiruddin et al., entitled “Lithium Ion Battery WithHigh Voltage Electrolytes and Additives,” incorporated herein byreference.

The electrodes described herein can be incorporated into variouscommercial battery designs. For example, the cathode compositions can beused for prismatic shaped batteries, wound cylindrical batteries, coinbatteries or other reasonable battery shapes. The batteries can comprisea single cathode structure or a plurality of cathode structuresassembled in parallel and/or series electrical connection(s).

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them and configured to form adesired battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors, and the resultingelectrode structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister is sealed to complete the battery. Desirable pouch batterydesigns are described further in copending U.S. provisional patentapplication 61/369,825 to Kumar et al., entitled “Battery Packs forVehicles and High Capacity Pouch Secondary Batteries for IncorporationInto Compact Battery Packs,” incorporated herein by reference.

Battery Performance

Batteries formed from the specific positive electrode active materialsdescribed herein have demonstrated superior performance under realisticdischarge conditions for moderate current applications. In particular,the doped active materials have exhibited high average dischargevoltages and high specific capacities upon cycling of the batteries atlow and moderate discharge rates. Based on the cycling results obtain inthe examples below and on related materials, it is expected that thematerials will exhibit good cycling properties out to relative longnumbers of cycles.

In general, various similar testing procedures can be used to evaluatethe battery performance. A specific testing procedure is described forthe evaluation of the performance values described herein. The testingprocedure is described in more detail in the examples below.Specifically, the battery can be cycled between 4.6 volts and 2.0 voltsat room temperature. The evaluation over the range from 4.6 volts to 2.0volts is desirable for commercial use since the batteries with activematerials described herein generally have stable cycling over thisvoltage range. In some embodiments, for the first two cycles, a batteryis discharged at a rate of C/10 to establish irreversible capacity loss.Then, the battery is cycled for two cycles at C/5, two cycles at C/3,five cycles at 1 C, five cycles at 2 C, five cycles at 5 C and threemore cycles at C/5. Again, the notation C/x implies that the battery isdischarged at a rate to discharge the battery to the selected voltagelimit in x hours. The battery capacity depends significantly on thedischarge rate, with reduced capacity as the discharge rate increases.

In some embodiments, the positive electrode active material can exhibita specific discharge capacity of at least about 260 mAh/g and in someembodiments at least about 270 mAh/g at a discharge rate of C/3 whendischarged from 4.6V to 2.0V. A person of ordinary skill in the art willrecognize that additional ranges of specific capacity and cyclingcapacity within the specific ranges above are contemplated and arewithin the present disclosure.

The average voltage of a material can be a significant parameter. Ahigher average voltage can indicate the ability to deliver additionalpower. In some embodiments with a lithium metal negative electrodeactive material, the average voltage can be at least about 3.60 volts,in further embodiments at least about 3.64 volts and in additionalembodiments at least about 3.65 volts, when discharged at a C/10 ratebetween 4.6 volts and 2.0 volts. In some embodiments of batteries, suchas pouch cells, with a graphitic carbon negative electrode activematerial, the average voltage can be at least about 3.45 volts, infurther embodiments at least about 3.475 volts and in additionalembodiments from about 3.50 volts to about 3.60 volts, when dischargedat a C/10 rate between 4.5 volts and 2.0 volts. Also, for the batterieswith a graphitic carbon negative electrode active material, the averagevoltage at the 250th discharge cycle can be at least about 3.25 volts,and in further embodiments at least about 3.3 volts and in additionalembodiments at least about 3.325 volts, when discharged at a C/3 ratebetween 4.5 volts and 2.0 volts. A person of ordinary skill in the artwill recognize that additional ranges of average voltage within theexplicit ranges above are contemplated and are within the presentdisclosure.

It is also useful to evaluate the DC resistance profiles as a functionof state of charge. The DC resistance from a 10 second pulse is definedas the change in voltage from the beginning of the pulse to the end ofthe pulse divided by the change in current at the beginning of the pulseand at the end of the pulse. The batteries described herein can exhibita DC resistance at a 1 hour rate (1C) in a 10 second pulse test for bothcharging and discharging that is no more than about 6 milliohms with astate of charge of at least about 30%, in other embodiments with a stateof charge at least about 25%, and in further embodiments with a state ofcharge of at least about 20%. In some embodiments, the batteries exhibita DC discharge resistance of no more than about 5 milliohms at a stateof charge of at least about 35%, in further embodiments at least about30% and in other embodiments at least about 25%. A person of ordinaryskill in the art will recognize that additional ranges of DC resistanceperformance within the explicit ranges above are contemplated and arewithin the present disclosure.

As noted above, the teachings herein provide for the design of a lithiumrich positive electrode composition with a desired balance ofproperties. While specific capacity tends to increase with increasingvalues of x, at least up to some value of x, other parameters, such aslong term cycling, average voltage and DC resistance tend to have moredesirable properties at lower values of x. An appreciation of thesedependencies has pointed to new composition ranges that can providesuperior performance for many applications of interest, such as vehicleapplications and consumer electronics.

EXAMPLES

The following examples are directed to the evaluation of ranges ofcompositions with selected amounts of metals being selected based on anoverall stoichiometry of LiMO₂, where M is a combination of metalelements Li, Ni, Co and Mn. Results are presented with and without acoating to stabilize the composition. The electrochemistry is alsostudied during the first charge/discharge step to elucidate thestoichiometric effects on the electrochemistry.

The coin cell batteries tested in Examples 3, 4 and 6 were performedusing coin cell batteries produced following a procedure outlined here.Example 7 describes battery performance results obtained using pouchbatteries, and the formation of the pouch batteries is described inExample 7. The lithium metal oxide (LMO) powders were mixed thoroughlywith acetylene black (Super P™ from Timcal, Ltd, Switzerland) andgraphite (KS 6™ from Timcal, Ltd) to form a homogeneous powder mixture.Separately, Polyvinylidene fluoride PVDF (KF1300™ from Kureha Corp.,Japan) was mixed with N-methyl-pyrrolidone (Sigma-Aldrich) and stirredovernight to form a PVDF-NMP solution. The homogeneous powder mixturewas then added to the PVDF-NMP solution and mixed for about 2 hours toform homogeneous slurry. The slurry was applied onto an aluminum foilcurrent collector to form a thin wet film.

A positive electrode material was formed by drying the aluminum foilcurrent collector with the thin wet film in vacuum oven at 110° C. forabout two hours to remove NMP. The positive electrode material waspressed between rollers of a sheet mill to obtain a positive electrodewith desired thickness. The mixture comprised at least about 75 weightpercent active metal oxide, at least about 3 weight percent acetyleneblack, at least about 1 weight percent graphite, and at least about 2weight percent polymer binder.

The positive electrode was placed inside an argon filled glove box forthe fabrication of the coin cell batteries. Lithium foil (FMC Lithium)having thickness of roughly 125 microns was used as a negativeelectrode. The electrolyte was selected to be stable at high voltages,and appropriate electrolytes are described in copending U.S. patentapplication Ser. No. 12/630,992, now published 2011/0136019 to Amiruddinet al., entitled “Lithium Ion Battery With High Voltage Electrolytes andAdditives,” incorporated herein by reference. A trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) soaked with electrolyte was placed betweenthe positive electrode and the negative electrode. A few additionaldrops of electrolyte were added between the electrodes. The electrodeswere then sealed inside a 2032 coin cell hardware (Hohsen Corp., Japan)using a crimping process to form a coin cell battery. The resulting coincell batteries were tested with a Maccor cycle tester to obtaincharge-discharge curve and cycling stability over a number of cycles.

Example 1 Synthesis of Lithium Rich Complex Metal Oxides

This example demonstrates the formation of a desired positive electrodeactive material using a carbonate or hydroxide co-precipitation process.Stoichiometric amounts of metal precursors were dissolved in distilledwater to form an aqueous solution with the metal salts in the desiredmolar ratios. Separately, an aqueous solution containing Na₂CO₃ and/orNH₄OH was prepared. For the formation of the samples, one or bothsolutions were gradually added to a reaction vessel to form metalcarbonate or hydroxide precipitates. The reaction mixture was stirred,and the temperature of the reaction mixture was kept between roomtemperature and 80° C. The pH of the reaction mixture was in the rangefrom 6-12. In general, the aqueous transition metal solution had aconcentration from 1 M to 3 M, and the aqueous Na₂CO₃/NH₄OH solution hada Na₂CO₃ concentration of 1 M to 4 M and/or a NH₄OH concentration of0.2-2M. The metal carbonate or hydroxide precipitate was filtered,washed multiple times with distilled water, and dried at 110° C. forabout 16 hrs to form a metal carbonate or hydroxide powder. Specificranges of reaction conditions for the preparation of the samples arefurther outlined in Table 1, where the solution may not include bothNa₂CO₃ and NH₄OH.

TABLE 1 Reaction Process Condition Values Reaction pH 6.0-12.0 Reactiontime 0.1-24 hr Reactor type Batch Reactor agitation speed 200-1400 rpmReaction temperature RT-80° C. Concentration of the metal salts 1-3MConcentration of Na₂CO₃ 1-4M Concentration of NH₄OH 0.2-2M   Flow rateof the metal salts 1-100 mL/min Flow rate of Na₂CO₃ & NH₄OH 1-100 mL/min

An appropriate amount of Li₂CO₃ powder was combined with the dried metalcarbonate or hydroxide powder and thoroughly mixed with a Jar Mill,double planetary mixer, or dry powder rotary mixer to form a homogenouspowder mixture. A portion, e.g. 5 grams, of the homogenized powders wascalcined in a step to form the oxide, followed by an additional mixingstep to further homogenize the powder. The further homogenized powderwas again calcined to form the highly crystalline lithium compositeoxide. Specific ranges of calcination conditions are further outlined inTable 2 (scfh is a standard cubic foot per hour).

TABLE 2 Calcination Process Condition Values 1^(st) Step temperature400-800° C. time 1-24 hr protective gas Nitrogen or Air Flow rate ofprotective gas 0-50 scfh 2^(nd) Step temperature 700-1100° C. time 1-36hr protective gas Nitrogen or Air Flow rate of protective gas 0-50 scfh

The positive electrode composite material particles thus formedgenerally have a substantially spherical shape and are relativelyhomogenous in size. The product composition was assumed to correspond tothe portions of the metal reactants used to form the composition withthe oxygen adjusting to yield the overall targeted oxidation state. Asdiscussed in the above sections, the overall formula for thesecompositions can be written as x Li₂MnO₃.(1−x) Li Ni_(u)Mn_(v)Co_(w)O₂(formula I) or Li_(1+b)Ni_(α)Co_(γ)Mn_(β)O₂ (formula II). Two sets ofcompositions were formed. For the first set, variations of compositionswere synthesized having u=v. As seen in Table 3, a total of 34 cathodecompositions ranging in X from 0.1 to 0.5 and in Mn % from 35% to 70%were synthesized. The relationship between the Ni, Co, and Mn present inthe compositions are further illustrated in FIG. 2. For the second setof compositions, u does not equal to v and again x=0.1, 0.2, 0.3, 0.4 or0.5. Table 4 shows 5 different synthesized cathode compositions andtheir corresponding Mn %.

TABLE 3 x Li Mn % Transition Composition Component Metals 1 0.500 68.752 0.500 67.25 3 0.500 65.62 4 0.500 64.12 5 0.500 62.50 6 0.500 59.37 70.500 56.25 8 0.500 53.12 9 0.500 50.00 10 0.400 62.54 11 0.400 60.62 120.400 58.82 13 0.400 56.90 14 0.400 51.26 15 0.400 41.90 16 0.300 56.2117 0.300 54.02 18 0.300 51.84 19 0.300 49.66 20 0.300 47.47 21 0.30043.10 22 0.300 38.74 23 0.300 34.37 24 0.300 30.00 25 0.200 50.05 260.200 47.52 27 0.200 44.99 28 0.200 42.46 29 0.200 34.98 30 0.200 22.5531 0.100 43.80 32 0.100 40.97 33 0.100 38.13 34 0.100 35.29

TABLE 4 x in Mn % Transition Composition xLi₂MnO₃•(1 − x)LiMO₂ Metal 350.5 65.63 36 0.4 58.75 37 0.3 51.90 38 0.2 45.49 39 0.1 38.13

The true density of the highly crystalline compositions was obtainedusing helium picnometry. Referring to FIG. 3, the densities are plottedas a function of the value of x in x Li₂MnO₃.(1−x) LiMO₂. While there isa slight scatter in the points, generally the true density is greaterfor compositions with lower amounts of X. Assuming that similar cathodeparticle morphology (particle size, porosity and surface area) can beobtained for the different X cathode compositions, a higher electrodedensity can be obtained for lower X compositions where the true densityis higher. With respect to obtaining a desired higher loading of powdersin the electrode, these respective properties can be appropriatelybalanced with other performance properties.

A portion of the compositions in both sets were coated with magnesiumoxide as a stabilization composition as described in Example 2 below.The coated and uncoated compositions were then used to form coin cellbatteries following the procedure outlined above. The coin cellbatteries were tested, and the results are described below in Examples 3(first set of compositions) and Example 4 (second set of compositions).

Additionally, a portion of the compositions from both set were coatedwith aluminum oxide as described in Example 5 below. The coated anduncoated compositions were then used to from coin cell batteriesfollowing the procedure outlined above. The coin cell batteries weretested, and the results are described below in Examples 6.

Example 2 Formation of MgO Coated Metal Oxide Materials

As described in this example, a portion of the LMO compositionssynthesized as described in Example 1 were coated with magnesium oxideas a stabilizing coating. Application of a magnesium oxide coating overLMO material was performed by drying a magnesium composition onto theLMO followed by a calcination step. Specifically, magnesium nitrate wasdissolved in a selected amount of water, and the positive electrodeactive material to be coated with MgO was dispersed in the magnesiumnitrate solution. Then, this mixture was heated at a sufficienttemperature for a few hours until reaching dryness. The dry powder wascollected and fired at a temperature from 300-500° C. for 1-5 h in aconventional muffle furnace in a dry air. The LMO coated with about 0.5wt % MgO were then used to form coin cell batteries following theprocedure outlined above. The coin cell batteries were tested, and theresults are described in examples below.

Example 3 Battery Performance—First Set of Compositions

This example demonstrates the battery performance of coin cells formedwith the lithium metal oxides with and without magnesium oxide coatingsfrom Examples 1 and 2 above.

Coin cells were formed with positive electrodes incorporating powderssynthesized as described in Examples 1 and 2. The coin cell batterieswere tested for 24 charge and discharge cycles at discharge rates ofC/10 for cycles 1-2, C/5 for cycles 3-4, C/3 for cycles 5-6, 1 C forcycles 7-11, 2 C for cycles 12-16, 5 C for cycles 17-21, and C/5 forcycles 22-24. Plots of specific discharge capacity versus cycle of thecoin cell batteries are shown in FIGS. 4-9 along with the specificdischarge capacity results for batteries with a second set ofcompositions described in Example 4 for comparison. Specifically, graphsshown in FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are directed tobatteries with positive electrode active materials with approximatestoichiometries represented by the formula I with x=0.1, 0.2, 0.3, 0.4,and 0.5, respectively. And FIG. 9 is directed to materials with x=0.5coated with 0.5 wt % MgO. Each figure consist of a set of plots withresults for the variations of compositions having varying degrees of Mn%. In general, the specific discharge capacity increased with increasingvalues of x in the formula for the positive electrode active material,but the batteries with the positive electrode material with x=0.5exhibited lower specific discharge capacities at higher rates relativeto batteries with the x=0.4 and x=0.5 coated with 0.5 wt % MgOmaterials.

Plots of differential capacity (mAh/V) versus voltage (V) of the coincell batteries are shown in FIGS. 10-14. Specifically, graphs shown inFIG. 10, FIG. 11, FIG. 12, FIG. 13, and FIG. 14 are directed to thedifferential capacities for batteries incorporating active materialsapproximately represented with formula I having x=0.1, 0.2, 0.3, 0.4,and 0.5 respectively. FIG. 14 also include data directed to compositematerial with x=0.5 coated with 0.5 wt % MgO. The charging process isplotted as a positive differential capacity, and the discharging processis plotted as a negative discharge capacity. For a particular value ofx, the differential capacity results are qualitatively the sameregardless of the amount of Mn %, although the differential capacitybehavior is strongly dependent on the value of X. The discharge peaknear 3.8-3.9 volts is believed to be related to the reaction of LiMO₂component of formula I, while the peak near 4.4-4.5 volts is believed tobe related to the reaction of the Li₂MnO₃ component of the composition.Thus, the peak near 3.8 volts diminishes and the peak near 4.4 voltsincreases as a function of increasing X.

Specific capacity at the first charge and discharge cycle, irreversiblecapacity loss and average voltage of the batteries are compared and theresults are outlined in Tables 5-9 below. As noted above, theirreversible capacity loss is the difference between the first chargecapacity and the first discharge capacity for the battery. The averagevoltage was obtained in the first discharge cycle for a discharge from4.6V to 2V at a discharge rate of C/10. Specifically, data shown inTable 5, Table 6, Table 7, Table 8, and Table 9 are directed to batteryperformance with positive electrode active materials with x=0.1, 0.2,0.3, 0.4, and 0.5 respectively. Each table includes a set of results forbatteries corresponding to cathode compositions with varying percent ofMn for a given X and results from corresponding composite materialscoated with 0.5 wt % MgO.

The variations of average voltage for batteries having activecompositions with different x values (0.1, 0.2, 0.3, 0.4, and 0.5) areplotted in FIG. 15. Specifically, average voltage decreased withincreasing x values for the positive electrode active material. Thevariation of first cycle discharge capacity at a rate of 0.1 C fordifferent x values (0.1, 0.2, 0.3, 0.4, and 0.5) are plotted in FIG. 16.Specifically, discharge capacity increased with increasing x values with0.4 and 0.5 having comparable discharge capacities. The values of IRCLincreased for increasing X values, as seen in FIG. 17. The increasingIRCL with increasing x values is consistent with the IRCL being mainlycontributed by the reaction of Li₂MnO₃.

TABLE 5 Average Specific Capacity (mAh/g) IRCL Voltage System ChargeDischarge (mAh/g) (V) Composition 31 230 202 28 3.866 Composition 31 231198 33 3.778 Coated Composition 32 227 200 27 3.893 Composition 32 237207 30 3.884 Coated Composition 33 230 200 30 3.879 Composition 33 233201 32 3.866 Coated Composition 34 233 205 28 3.893 Composition 34 227200 27 3.883 Coated

TABLE 6 Average Specific Capacity (mAh/g) IRCL Voltage System ChargeDischarge (mAh/g) (V) Composition 25 249 211 38 3.782 Composition 25 252210 42 3.773 Coated Composition 26 253 218 35 3.803 Composition 26 252209 43 3.743 Coated Composition 27 247 212 35 3.784 Composition 27 259218 41 3.783 Coated Composition 28 254 220 34 3.796 Composition 28 267228 39 3.776 Coated Composition 29 242 206 36 3.819 Composition 30 266225 41 3.767

TABLE 7 Average Specific Capacity (mAh/g) IRCL Voltage System ChargeDischarge (mAh/g) (V) Composition 16 281 232 49 3.659 Composition 16 288232 56 3.676 coated Composition 17 273 226 47 3.678 Composition 17 292235 57 3.7 coated Composition 18 272 228 44 3.681 Composition 18 292 23656 3.704 coated Composition 19 271 228 43 3.717 Composition 19 291 23853 3.718 coated Composition 20 292 255 37 3.706 Composition 21 294 25440 3.701 Composition 22 299 259 40 3.684 Composition 23 298 253 45 3.676Composition 24 302 246 57 3.661

TABLE 8 Average Specific Capacity (mAh/g) IRCL Voltage System ChargeDischarge (mAh/g) (V) Composition 10 315 252 63 3.682 Composition 10 318255 63 3.666 Coated Composition 11 322 265 57 3.649 Composition 11 323264 59 3.636 Coated Composition 12 317 261 56 3.659 Composition 12 323264 59 3.644 Coated Composition 13 317 268 49 3.638 Composition 13 322268 54 3.635 Coated Composition 14 315 277 38 3.622 Composition 15 326246 81 3.614

TABLE 9 Average Specific Capacity (mAh/g) IRCL Voltage System ChargeDischarge (mAh/g) (V) Composition 1 327 258 69 3.578 Composition 1 331260 71 3.595 coated Composition 2 331 261 70 3.576 Composition 2 340 27070 3.586 coated Composition 3 332 257 75 3.575 Composition 3 340 267 733.59 coated Composition 4 331 260 71 3.565 Composition 4 328 258 703.586 coated Composition 5 339 239 100 3.533 Composition 6 345 249 963.567 Composition 7 345 223 123 3.5294 Composition 8 356 218 133 3.533Composition 9 351 217 133 3.5145

Differential capacity (mAh/V) versus voltage (V) of the coin cellbatteries with different values of X are compared in FIG. 18. Thedifferential capacity curves shown in FIG. 18 show a peak at about 4.4volts decreasing in magnitude for the lower X compositions. However, thepeak near 3.8-4.0 volts increases in magnitude and shifts with respectto voltage for lower X compositions.

Example 4 Battery Performance—Second Set of Compositions

This example demonstrates the battery performance of coin cells formedwith the lithium metal oxides with the set of compositions from Example1, with or without magnesium oxide coatings as specified in Example 2above.

Coin cells were formed with positive electrodes incorporating powderssynthesized as described in Examples 1 and 2. The coin cell batterieswere tested for 19 charge and discharge cycles at discharge rates ofC/10 for cycles 1-2, C/3 for cycles 3-4, 1 C for cycles 5-9, 2 C forcycles 10-14, and 5 C for cycles 15-19. The battery with composition 35had an extra two C/5 cycles in comparison with the batteries with theother compositions. Plots of specific discharge capacity versus cyclenumber of the coin cell batteries incorporating active materialsapproximately represented with formula I having x=0.1, 0.2, 0.3, 0.4 and0.5 are shown in FIG. 19. In general, the specific discharge capacityincreased with increasing values of x in the formula for the positiveelectrode active material, but the batteries with the positive electrodematerial with x=0.4 exhibited lower specific discharge capacities athigher rates relative to batteries with the x=0.1, 0.2, and 0.3.

Plots of differential capacity (mAh/V) versus voltage (V) of the coincell batteries incorporating active materials approximately representedwith formula I having x=0.1, 0.2, 0.3, 0.4 and 0.5 are shown in FIG. 20for charge and discharge cycle 2. The charging process is plotted as apositive differential capacity, and the discharging process is plottedas a negative discharge capacity. The discharge peak near 3.8-3.9 voltsis believed to be related to the reaction of LiMO₂ component of formulaI, while the peak near 3.0 volts is believed to be related to thereaction of the Li₂MnO₃ component of the composition. Thus, the peaknear 3.8 volts diminishes and the peak near 3.0 volts increases as afunction of increasing X.

Specific capacity at the first charge and discharge cycle, irreversiblecapacity loss and average voltage of the batteries incorporatingpositive electrode active materials with x=0.1, 0.2, 0.3, 0.4 and 0.5are compared and the results are outlined in Table 10 below. As notedabove, the irreversible capacity loss is the difference between thefirst charge capacity and the first discharge capacity for the battery.The average voltage was obtained in the first discharge cycle for adischarge from 4.6V to 2V at a discharge rate of C/10.

TABLE 10 1^(st) 1^(st) Irre- Charge Discharge versible Avg. x inCapacity Capacity loss Voltage xLiMn₂O₃•(1 − x)LiMO₂ (mAh/g) (mAh/g)(mAh/g) (V) 0.1 235 203 32 3.867 0.2 259 214 45 3.810 0.3 294 245 493.711 0.4 316 270 46 3.606 0.5 330 268 58 3.6

Example 5 Formation of AlF₃ Coated Lithium Metal Oxide Materials

The lithium metal oxide particles prepared in the example 1 were coatedwith a thin layer of aluminum fluoride (AlF₃) using a solution-basedmethod. For a selected amount of aluminum fluoride coating, anappropriate amount of saturated solution of aluminum nitrate wasprepared in an aqueous solvent. The lithium metal oxide particles werethen added into the aluminum nitrate solution to form a mixture. Themixture was mixed vigorously for a period of time to homogenize. Thelength of mixing depends on the volume of the mixture. Afterhomogenization, a stoichiometric amount of ammonium fluoride was addedto the homogenized mixture to form aluminum fluoride precipitate whileretaining the source of fluorine. Upon the completion of theprecipitation, the mixture was stirred at 80° C. for 5 h. The mixturewas then filtered and the solid obtained was washed repeatedly to removeany un-reacted materials. The solid was calcined in nitrogen atmosphereat 400° C. for 5 h to form the AlF₃ coated lithium metal oxide material.

Samples of lithium metal oxide (LMO) particles synthesized as describedin example 1 were coated with various selected amounts of aluminumfluoride using the process described in this example. Transmissionelectron microscopy was used to assess the thickness of the resultingAlF₃ coatings. The aluminum fluoride coated LMOs were then used to formcoin cell batteries following the procedure outlined above. The coincell batteries were tested as described in the following Example 6.

Example 6 Battery Performance for AlF₃ Coated Samples

This example demonstrates how the battery performance varied withrespect to different lithium metal oxide compositions for a range ofAlF₃ coating thicknesses and for various battery performance parameters.

Coin cell batteries were formed from the materials synthesized asdescribed above. The cells were cycled to evaluate their performance.The first three cycles were measured at a charge/discharge rate of 0.1C. The next three cycles were measured at a charge/discharge rate of 0.2C. The subsequent cycles were measured at a charge/discharge rate of0.33 C. Specific capacity versus cycle of the coin cell battery areshown in FIG. 21. The battery maintained approximately 98% specificcapacity after going through 40 charge and discharge cycles relative tothe 7th cycle specific capacity.

Specific capacity versus cycle of the coin cell batteries formed fromuncoated, 3 nm, 6 nm, 11 nm, 22 nm, and 40 nm aluminum fluoride coatedLMO materials were tested and the results are shown in FIG. 22.Batteries with the coated LMO materials showed a complex relationshipbetween specific capacity performances as a function of the coatingthickness. Batteries with LMO materials having a 6 nm aluminum fluoridecoating had the highest specific capacity at low cycle number, whilebatteries with LMO materials having a 4 nm aluminum fluoride coating hadthe highest capacity at 40 cycles. Battery with LMO materials having 40nm coating had the lowest specific capacity, which was lower than thebattery with the uncoated material, but this battery exhibited a slightincrease in capacity with cycling.

The first cycle irreversible capacity loss (IRCL) of the batterieshaving uncoated, 3 nm, 6 nm, 11 nm, 22 ma, and 40 nm aluminum fluoridecoated LMO materials were measured. A plot of the results in percentageof overall capacity versus coating thickness is shown in FIG. 23 a and aplot of the results in specific capacity change as a function of coatingthickness is shown in FIG. 23 b. The IRCL results showed a steadydecrease of the IRCL for batteries with coating thicknesses of about 10nm, and the IRCL roughly leveled off with for batteries having 11 nm, 22nm, and 40 nm aluminum fluoride coated LMO materials.

The average voltages of the batteries were measured for batteries havingpositive electrodes with uncoated, 3 nm, 6 nm, 11 nm, 22 nm, and 40 nmaluminum fluoride coated LMO materials. The average voltage was takenover a discharge from 4.6V to 2.0V. A plot of average voltage as afunction of coating thickness is shown in FIG. 24 a, and a plot ofpercentage of voltage reduction relative to the uncoated materialperformance versus coating thickness is shown in FIG. 24 b. The averagevoltage generally showed a decrease versus increased aluminum fluoridecoating thickness on the LMO materials, although the decrease in averagevoltage was small for coatings of 6 nm or less.

Additionally, the coulombic efficiency of the batteries having uncoated,3 nm, 6 nm, 11 nm, 22 nm, and 40 nm aluminum fluoride coated LMOmaterials were measured. As used here, the coulombic efficiency isevaluated as the specific capacity at cycle 40 as a percentage of thespecific capacity at cycle 7, the first cycle at a rate of C/3. In otherwords, the coulombic efficiency is 100×(specific capacity at cycle40)/(specific capacity at cycle 7). A plot of the coulombic efficiencyas a function of coating thickness is shown in FIG. 25. The coulombicefficiency increased by about 2% when coating thickness is increasedfrom zero to 3 nm The coulombic efficiency then decreased significantlywhen coating thickness is increased from 3 nm to 6 nm and 11 nm Thecoulombic efficiency increased dramatically for batteries formed withpositive electrode active materials when the coating thickness was 22 nmand 40 nm.

Example 7 Performance Results with Pouch Batteries

This example provides results based on pouch batteries with roughly 20Ah total capacity with representative lithium rich active compositionssynthesized as described in Example 1.

The lithium metal oxide (LMO) powders were synthesized as described inExample 1. Representative powders with X=0.2, 0.3, 0.4 and 0.5 were usedto form pouch batteries. The LMO powder was mixed thoroughly withacetylene black (Super P™ from Timcal, Ltd, Switzerland) and graphite(KS 6™ from Timcal, Ltd) to form a homogeneous powder mixture.Separately, Polyvinylidene fluoride (PVDF) (KF1300™ from Kureha Corp.,Japan) was mixed with N-methyl-pyrrolidone (NMP)(Honeywell—Riedel-de-Haen) and stirred overnight to form a PVDF-NMPsolution. The homogeneous powder mixture was then added to the PVDF-NMPsolution and mixed to form homogeneous slurry. The slurry was appliedonto an aluminum foil current collector to form a thin wet film using ablade coating process.

A positive electrode structure was formed by drying the aluminum foilcurrent collector with the thin wet film in vacuum oven to remove NMP.The positive electrode and the foil current collector were pressedtogether between rollers of a sheet mill to obtain a positive electrodestructure with desired thickness. The average thickness with the foilfor the cathodes was roughly 110 microns.

A blend of graphite and binder was used as the anode (negativeelectrode), and the negative electrode composition was coated onto acopper foil current collector. The polymer binder was a blend ofstyrene-butadiene rubber (SBR) and carboxymethyl cellulose. The foil andanode paste were pressed together between rollers of a sheet mill. Thecompleted anodes had a total thickness with the foil of roughly 115microns.

The battery was constructed with 24 anode plates alternating with 23cathode plates such that an anode plate is positioned at both ends ofthe stack. A trilayer (polypropylene/polyethylene/polypropylene)micro-porous separator (2320 from Celgard, LLC, NC, USA) soaked withelectrolyte was placed between adjacent anodes and cathodes. Theelectrolyte was selected to be stable at high voltages, and appropriateelectrolytes are described in copending U.S. patent application Ser. No.12/630,992, now published 2011/0136019 to Amiruddin et al., entitled“Lithium Ion Battery With High Voltage Electrolytes and Additives,”incorporated herein by reference. The electrode stack was then assembledinto a conventional pouch cell structure. The resulting pouch batteryhad dimensions of 203 mm×93 mm×7.1 mm The battery had a room temperaturedischarge capacity of 15.3 Ah at a discharge rate of C/3. The formationof pouch cells using lithium rich positive electrode active compositionsis described further in copending provisional U.S. patent applicationSer. No. 61/369,825 to Kumar et al., entitled “Battery Packs forVehicles and High Capacity Pouch Secondary Batteries for Incorporationinto Compact Battery Packs,” incorporated herein by reference.

The DC-resistance was measured for the pouch batteries as a function ofthe state of charge for representative cathode compositions with X=0.3,X=0.4 and X=0.5. To perform further pulse testing, the battery ischarged to 4.5V and then subjected to 1 C Pulse Test at room temperature(23° C.) with 10 second pulses. In the pulse test, the DC resistance wasevaluated as a function of the state of charge starting from an initial90% state of charge. The DC-resistance data is shown in FIG. 26.

While desirable values of DC-resistance below about 6 milliohms (mΩ) areobtained with all of the batteries for greater states of charge, theresistance increases as the state of charge decreases. However, theDC-resistance increases more slowly as a function of the state of chargefor positive electrode compositions with lower values of X. Thus,batteries formed with compositions with lower values of X can bedischarged in commercial applications down to lower values of chargewith desired low values of resistance before recharging the battery. Theresistance was less than about 5 milliOhms (mΩ) for a state of chargegreater than about 35% for all three batteries and less than about 10 mΩfor a state of charge greater than about 18% for all three batteries.Therefore, the batteries exhibit very low DC resistance down to lowstates of charge. Low DC resistances can reduce heat generation in abattery pack, which can be desirable especially for vehicleapplications.

Example 8 Performance of Coin Batteries with Graphitic Carbon Anodes

Coin cells were also formed with graphitic carbon anodes to test thecycling performance at longer numbers of cycles.

Coin cells were formed as described above except that the negativeelectrodes were formed as follows. The negative electrode comprisedgraphite as the active material.

To form the negative electrode, Super P™ acetylene black was mixed withNMP, and PVDF binder (KF9305™ from Kureha Corp., Japan) was added to theNMP and stirred. Graphitic material was added to the solution andstirred. The negative electrode composition was coated onto a copperfoil current collector and dried. The negative electrode was thenpressed to a desired thickness.

Coin batteries formed with cathode materials having X=0.2, X=0.3 andX=0.5 were cycled between 4.5V and 2 volts for 225, 350 and 400 cycles,respectively. The first two cycles were performed at a rate of C/10, andsubsequent cycles were performed at a rate of C/3. The specificdischarge capacities are plotted in FIG. 27. While the batteries withthe X=0.5 compositions has significantly greater specific capacityinitially, these batteries also exhibited faster fade of capacity withcycling. At 225 cycles, the cycling efficiencies with respect tospecific capacity for the batteries relative to the initial cyclingperformance were about 90% for X=0.2, 87% for X=0.3 and 81% for X=0.5.Similarly, the average voltages were measured for these batteries withcycling. The average voltage as a function cycle number is plotted inFIG. 28 for the three coin batteries. The batteries formed with theX=0.5 cathode composition exhibited a significantly lower averagevoltage at all cycles relative to the other two batteries, and theaverage voltage dropped more quickly with cycling for the battery withthe X=0.5 cathode material. A lower average voltage generally results ina corresponding decrease in energy and power available from the battery.The battery with the X=0.2 composition exhibited just a slightly greateraverage voltage at all of the cycles relative to the average voltageexhibited by the battery with X=0.3.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein. As used herein, the notation(value1≦variable≦value2) implicitly assumes that value 1 and value 2 areapproximate quantities.

What is claimed is:
 1. A positive electrode active composition for alithium ion battery comprising a layered lithium metal oxideapproximately represented by the formula x Li₂MnO₃.(1−x) LiNi_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂, x is at least about 0.35 and no more thanabout 0.425, the absolute value of Δ generally is no more than about0.3, 2u+w+y is approximately equal to 1, w is in the range from 0 to 1,u is in the range from 0 to 0.5 and y is no more than about 0.1, withthe proviso that both (u+Δ) and w are not zero, wherein an optionalfluorine dopant can replace no more than about 10 mole percent of theoxygen.
 2. The positive electrode active composition of claim 1 theabsolute value of Δ generally is no more than about 0.2, w is at leastabout 0.1 and no more than about 0.6, u is at least about 0.1 and nomore than about 0.45
 3. The positive electrode active composition ofclaim 1 the absolute value of Δ generally is no more than about 0.15, wis at least about 0.2 and no more than about 0.475, u is at least about0.2 and no more than about 0.4 and y is approximately
 0. 4. The positiveelectrode active composition of claim 1 wherein the positive electrodeactive material is approximately represented by the formulaLi_(1+b)Ni_(α)Co_(γ)Mn_(β)O₂, where b ranges from about 0.149 to about0.173, α ranges from 0 to about 0.4, γ ranges from 0 to about 0.46, βrange from about 2b+α−0.2 to about 2b+α+0.2 with the proviso that both αand γ are not zero, where b+α+β+γ is approximately equal to
 1. 5. Thepositive electrode active composition of claim 1 further comprising acoating having a different composition from the active composition. 6.The positive electrode active composition of claim 1 further comprisinga coating comprising a metal oxide.
 7. The positive electrode activecomposition of claim 1 having a specific discharge capacity of at leastabout 235 mAh/g cycled from 4.6 volts to 2.0 volts at a rate of C/3. 8.The positive electrode active composition of claim 1 having a specificdischarge capacity of at least about 190 mAh/g cycled from 4.6 volts to2.0 volts at a rate of 1 C.
 9. The positive electrode active compositionof claim 1 having an average voltage of at least about 3.64 cycledbetween 4.6 volts and 2.0 volts.
 10. The positive electrode activecomposition of claim 1 having a first cycle irreversible capacity lossupon charging to 4.6V of no more than about 65 mAh/g.
 11. A batterycomprising a negative electrode, a positive electrode comprising thepositive electrode active composition of claim 1, a separator betweenthe positive electrode and the negative electrode, and an electrolytecomprising lithium ions.
 12. The battery of claim 11 wherein thenegative electrode comprises graphitic carbon.
 13. A method forsynthesizing a positive electrode active composition, the methodcomprising: co-precipitating a precursor composition comprisingmanganese as well as nickel and/or cobalt in selected amountscorresponding to a product composition approximately represented by theformula x Li₂MnO₃.(1−x) Li Ni_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂, x is at leastabout 0.35 and no more than about 0.425, the absolute value of Δgenerally is no more than about 0.3, 2u+w+y is approximately equal to 1,w is in the range from 0 to 1, u is in the range from 0 to 0.5 and y isno more than about 0.1 with the proviso that both (u+Δ) and w are notzero, wherein an optional fluorine dopant can replace no more than about10 mole percent of the oxygen; adding a lithium source at a selectedpoint in the process; and heating the precursor composition to decomposethe precursor composition to form a metal oxide.
 14. The method of claim13 wherein the precursor composition comprises an hydroxide.
 15. Themethod of claim 13 wherein the precursor composition comprises acarbonate.
 16. The method of claim 13 wherein the lithium source isblended with the precursor composition prior to the decomposition of theprecursor composition to form the metal oxide.
 17. The method of claim13 wherein the heating to decompose the precursor composition isperformed to a first temperature, and further comprising heating themetal oxide to a second temperature greater than the first temperatureto improve the crystallinity of the metal oxide.
 18. A positiveelectrode active material for a lithium ion cell comprising a layeredlithium metal oxide approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2-z)F_(z), where b ranges from about0.149 to about 0.173, α ranges from 0 to about 0.4, β range from about0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0to about 0.15 and z ranges from 0 to 0.2, with the proviso that both αand γ are not 0, and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti,Ca, Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof, and having adischarge capacity at the 10th cycle that is at least about 170 mAh/gwhen discharged at room temperature at a discharge rate of 2 C.
 19. Thepositive electrode active material of claim 18 having a dischargecapacity at the 10th cycle that is at least about 180 mAh/g whendischarged at room temperature at a discharge rate of 2 C.
 20. Thepositive electrode active composition of claim 18 further comprising acoating having a different composition from the active composition. 21.The positive electrode active composition of claim 18 having a specificdischarge capacity of at least about 235 mAh/g cycled from 4.6 volts to2.0 volts at a rate of C/3.
 22. The positive electrode activecomposition of claim 18 having a specific discharge capacity of at leastabout 190 mAh/g cycled from 4.6 volts to 2.0 volts at a rate of 1 C. 23.The positive electrode active composition of claim 18 having an averagevoltage of at least about 3.64 cycled between 4.6 volts and 2.0 volts.24. The positive electrode active composition of claim 18 having a firstcycle irreversible capacity loss upon charging to 4.6V of no more thanabout 65 mAh/g.